Study of Seismic Anomalies in the Frequency Spectrum as a Hydrocarbon Reservoir Characterizer

Abstract

In this investigation, the variation of the frequency-dependent seismic response product of changes in fluid saturation and gas-to-oil ratio (GOR) was analyzed through the development of two synthetic models and the analysis of field data. The fields of study were the Powder River Basin and the Stratton Field located in the United States. The fluid´s substitution was carried out applying the Gassmann´s Equation (1951), allowing to estimate Vp, Vs and density for reservoirs with different properties. The petrophysical parameters used in the fluid’s substitution were defined by an analysis of well logs located in the Powder River Basin. In order to study the relationship between frequency and fluid content, the attributes of instantaneous frequency and Continuous Wavelet Transform method were used. It was found that there is a complex relationship between frequency-dependent reflections and fluid saturation in reservoirs. Observations made through mathematical models and field data suggest that (1) the presence of gas, both in oil reservoirs and in its gaseous state, generate an increase in the energy of the reflections (bright spot) and produce low frequency anomalies, (2) these effects are accentuated in porous and permeable media, (3) they increase exponentially in the presence of free gas and (4) is attributed to areas with a low Vp/Vs ratio. In addition, it was concluded that the joint use of the attributes of instantaneous amplitude and instantaneous frequency can be competent to monitor changes in gas/water saturation.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019